Monitoring local seismicity using a Distributed Fiber Optic Sensing (DFOS) measuring station in the Munich region

Distributed Fiber Optic Sensing (DFOS) refers to an ensemble of sensing techniques making it possible to turn an optical fiber into a vast network of equally spaced sensors. Among these methods, Distributed Acoustic Sensing (DAS) allows the acquisition of broadband seismic data while interrogating long profiles with a dense spatial and temporal sampling. Thus, DAS provides access to new capabilities in terms of near-surface measurements, especially regarding monitoring and logging.

In the framework of the INSIDE project (BMWK project) a DAS measurement station was installed in the municipality of Buchenhain (Landkreis München) with the purpose of monitoring locally induced seismicity. The DAS system is operated on fiber optic cables deployed near the surface and in a dedicated 250 m deep well, allowing seismic signals of different directivities to be recorded at the same location. At the station, Distributed Strain Sensing (DSS) is acquired on the same fiber optic cable with the aim to monitor processes characterized by low frequencies. In addition, a broadband seismometer is deployed to offer further processing possibilities and a comparative reference.
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Based on local and regional seismic events, we discuss the detection and localisation capabilities of the DAS monitoring station with regards to its urban location. We discuss the complementary role of DAS to the surface seismometer-based monitoring network, particularly with respect to the spatial continuity of the DAS recordings, which provides a beneficial insight into the seismic monitoring. Finally, we discuss the possibilities of the joint deployment of the cable at the surface and in the well to overcome the limitations of DAS in terms of directionality, with the objective of resolving the back-azimuth of seismic events.